Thoroughly search scrub (5)
I believe the answer is:
scour
I believe this is a double definition.
'thoroughly search' is the first definition.
(I've seen this before)
'scrub' is the second definition.
(I know that scrub can be written as scour)
(Other definitions for scour that I've seen before include "Look high and low" , "Rub hard or search thoroughly" , "Clean - scout" , "Clean by abrasion" , "Scrub clean" .)