As a follow-up you can tell what domain the user is in by looking at the FEDB query and then looking at the string after the mailbox number and ext number. in the case below you will see the first one starts with a 0C0 and all of the others are B60 The 0C0 is a different domain in the VMD. I have removed the names from this list so it will look different when you run it.
umObjectGUID=27a83a6c7e1511db9c6f000423c1b467,ou=People,dc=Avaya",7258,7258,0C01679D-E882-406E-9EEF-96279BD8C5FD,7258,**Password**,0,1,0,0,1,3,1
umObjectGUID=f740ebbd131a4bda91eefaa60eea7316,ou=People,dc=Avaya",6466,6466,B6027C7A-63F1-4B5B-83FD-0A8B7E0F1CDD,6466,**Password**,2048,1,0,0,1,3,1
umObjectGUID=2aba355efad1483fb0678a84061b68b0,ou=People,dc=Avaya",7481,7481,B6027C7A-63F1-4B5B-83FD-0A8B7E0F1CDD,7481,**Password**,2048,1,0,0,1,3,1
umObjectGUID=8b7cfbd3e619404288c62b94e4db6008,ou=People,dc=Avaya",7551,7551,B6027C7A-63F1-4B5B-83FD-0A8B7E0F1CDD,7551,**Password**,2048,1,0,0,1,3,1
Ken Means
"I find that the harder I work, the more luck I seem to have."
- Thomas Jefferson (1743-1826)