Do you mean one of the liquid metal ones? Goes on with syringe and spreads out over the IHS?
If so, your options are limited. The liquid runs into the cracks in the surface in the same fashion of solder wetting copper. This is part of why it works so well as a tim. It also means the only convincing means of removing the stuff is lapping.
You can use normal paste on top of it without ill effect, but the IHS will still look stained. Or you can use more of the same liquid. If you're selling it, the buyer may be twichy about it having a really high end thermal interface material filling the voids within the surface, but if so the same buyer probably doesn't want it lapped either.
I remove standard paste with alcohol, but I'm pretty certain that won't touch the metallic stuff. I just leave it on the cpu.
Not really the answer you wanted