1. To wash the inside of something very thoroughly and vigorously. A noun or pronoun can be used between "scrub" and "out." Did you scrub out the pots and pans like I asked? I've got to take this apart and scrub it out from the inside.

2. To clean some substance or residue out of the inside of something very thoroughly and vigorously. A noun or pronoun is used between "scrub" and "out"; often followed by "of (something)." You can't just leave the pot to soak overnight—you've got to scrub all the burnt food out with a scouring pad. I've got to scrub the gunk out of my keyboard, or it could end up permanently broken.