Isoproply alcohol over %70
not rubbing alcohol
rubbing alcohol is diluted with fragrances and menthol
for smell and soothing
Isoproply is cleaner
also can use coffee filters for wipe up
clean paper with no fragrance chemicals
remember that anything that can leave an oily residue
inlcuding your fingers can affect the cpu
also if the paste is dried on and cool on the CPU
then heat up with a hand held blow dryer
use an old credit card to scrape off thermal paste
(plastic wont damage CPU)
Alcohol Prep Pads for site injections is what I normally use, they're 70% Isopropyl Alcohol and Sterile Water, they're the perfect size and very convenient.
If it's really bad you can use old school fingernail polish remover, which is Acetone and Distilled water, old school meaning it doesn't have a massive amount of additives, like Vitamin E, Fragrances, etc..
Use Q-tips to scrub tough areas with the Fingernail Polish Remover.
Finish with and Alcohol Prep Pad, and immediately dry with short spray of canned air which is normally co2, dries the alcohol instantly, and blows any loose fibers off.