title: List all unused domains for a Firebird database
body: <p>Is there a quick way to list all Firebird domains defined for a database that are actually not used by any field ? I have a large database with many tables and many domains and it seems that a lot of them are not anymore used, so I guess it's time for a cleanup !</p>
  
  <p>I think this is possible by querying the <code>RDB$...</code> system tables, but I'm unsure how to do this.</p>