Arctic Silver thermal compound can easily be removed from hardware using the proper cleaners and tools. For general clean-up, a cloth or paper towel will work well. Intricate cleaning can be accomplished with Q-tip swabs. An old toothbrush can often get the compound out of crevices that other tools cannot reach.
The recommended cleaners are:
CPU Core:
ArctiClean 1 Thermal Material Remover followed by ArctiClean 2 Thermal Surface Purifier. If you do not have ArctiClean, use high-purity isopropyl alcohol or acetone and a bit of careful rubbing.
Do not use nail polish remover as it contains fragrance oils and other contaminants.
(If you use acetone, do a final cleaning with isopropyl alcohol.)