Clean with hard rubbing (5)
I believe the answer is:
scrub
'clean with hard rubbing' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for scrub that I've seen before include "Cancel; clean vigorously" , "stunted trees and brushwood" , "Cancel (colloq)" , "Vegetation consisting of stunted trees or bushes" , "Rub hard; brushwood" .)