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'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.
I think the best way would be to provide an option to make the same question visible across multiple SE communitites without a need to re-create the question in other communitites (which they are doing now). The answers also can be made visible across the sites. I am saying this because I have myself done that a couple of times just for a straightforward reason: I wanted my question to be visible to more number of people and I found the subject valid in multiple communities.