The only thing that I found will remove artic silver is engine degreaser, its about a dollar for a can and works great. I've done this to 3 cpus, no problems, I usually spray it on the top, wipe with a towel, and finish it off with isopropyl alcohol, heck one time I just soaked it in the degreaser and alcohol and let it dried it with compressed air and it still worked.
Alex