Question: A few seconds ago a first time user of AU asked a question (on AU), which was promptly and correctly [answered](https://askubuntu.com/questions/794013/what-is-in-terminal-command-line) by @terdon. That question had an [exact dupe](https://unix.stackexchange.com/questions/11376/what-does-double-dash-mean-also-known-as-bare-double-dash), equally well answered by @Guss, earlier on Unix & Linux, a SE communities with *some* overlap with AU and a few other SE communities.

Initially I was actually real surprised that said question was not already answered on AU; on second thought it actually *made sense* since it already had at least one excellent answer on Unix & Linux. 

It *made sense*, **but** I would not go as far as saying that before making a query on AU, one should first check whether there is an answer for it in a different SE community. Rather one should learn to post in the right community to begin with. Right, but sometimes it's not so easy to decide as in this case.

* So, how should one treat a query in a community A, which was already posted in unequivocal terms in community B, both on SE ?
* Should one call that a dupe or a "cross-dupe", without meaning that the two communities are one but somehow closely related ? I am not sure that sounds completely right.
* Should flair be awarded per usual, either through upvotes or automatic increment upon acceptance of such an answer to a cross-dupe ?
* Or should the query echoing another identical query in another community of StackExchange be treated differently in terms of flair accrual, categorisation as dupe, removal, etc. ?

Answer: 
I think a lot of the confusion arises from forums that are very similar. In some cases, a question is on topic in more than one community. In that case, I believe that exact duplicates **should** stay. I have basically two reasons:

1. Web presence
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If the question is correctly answered in two places, the answer will be easier for people to find straight from the search engine or even straight on the site. In other words, whether a person is searching Google for an answer to a question or searching a particular StackExchange community, they will find the information.

2. Bigger database
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It also gives each stackexchange communtiy a larger database of information to draw from in the future, preventing further confusion. That is to say, even if you were somehow able to close all these remotely duped questions, sooner or later, it's going to pop up again and you'll have to do it again. Wastes time: poor moderators.

All that being said, I have seen situations arise in which a question is questionably on topic but and is already correctly answered in a community where it is unquestionably **on topic**. In these cases, my humble opinion is that there should be a means of migrating and duping. Otherwise, it simply promotes re-asking questions in the wrong place; thus promoting disorder and cheating the system.
I'm on the fence on this one more leaning toward the some overlap argument as a certain amount of overlap between here and U&L is unavoidable and likely positive, but Braiam does make an excellent point regarding due diligence. As it is, when I run across a question that I know has been answered (and answered well) on another SE site I just comment and point to the related answer rather than wasting valuable time re-answering. In fact if I'm doing MY due diligence I will discover the existing answer on another SE site resulting in the same action as if I had prior knowledge. Sometimes (often?) the question has been answered partially on a number of sites in which case I do my best to pull all the information together and cite the sources. I don't think different methods of determination or handling of cross-dupes are necessary.