To clean away some substance or residue (from something) very thoroughly and vigorously. A noun or pronoun is used between "scrub" and "off." You should be scrubbing off all the caked-on dirt and grime from your bicycle at least once a week, or it will wear out a lot faster than it would otherwise. The salt-and-sugar rub helps you scrub dirt and dead skin cells off your body, giving your skin a bright, healthy glow.