Shah's domain, once
I believe the answer is:
iran
'shah's domain once' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for iran that I've seen before include "It used to be Persia" , "Country lying to south of Caspian sea" , "Nation" , "Tehran's country" , "Country where ayatollahs replaced a shah" .)