scrub vs scrub up

scrub is a noun but scrub up is not a noun.

Word	Noun	Adjective	Verb	Adverb
scrub	Yes	Yes	Yes	No
scrub up	No	No	Yes	No

As verbs, scrub and scrub up are synonyms defined as:

scrub (noun)	scrub up (noun)
the act of cleaning a surface by rubbing it with a brush and soap and water
dense vegetation consisting of stunted trees or bushes

scrub (adjective)	scrub up (adjective)
(of domestic animals) not selectively bred

scrub (verb)	scrub up (verb)
wash thoroughly	wash thoroughly
clean with hard rubbing
postpone indefinitely or annul something that was scheduled