just use a tissue.... no real need to get every last spec of it off with alcohol.
Actually you should get every last speck off... because a small piece or lump of dried thermal paste can cause a problem and leave a very small gap. I just swapped a Core 2 chip a few weeks ago, and didn't clean it perfectly... the computer started shutting off and running hot, but the stock Intel heatsink was flush against the CPU and all the clips were firmly mounted. I took it back off and noticed some of the original grey paste from Intel was hard and keeping it from making a smooth contact. I cleaned it off completely then re-apply new thermal paste. No problems now.