Territory over which control is exercised (6)
I believe the answer is:
domain
'territory over which control is exercised' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for domain that I've seen before include "estate" , "Area under someone's control, field of activity" , "Territory over which rule or control is exercised" , "Kingdom or realm" , "Field of thought or activity" .)