I had to think about this one a bit, but I'm going to say rose quartz, fluorite, or grounding stones such as obsidian.
For me personally it would depend on what exactly I am trying to cleanse the deck of
I would use rose quartz to "heal" my deck of past readings with less than positive energies and infuse it with love, fluorite to "freshen up" my deck if nothing negative had come up recently - just a routine cleanse, and obsidian to draw out any very negative energies imparted to it by a less than pleasant querent. I would also use obsidian in the case that my deck has been seeing a lot of action lately, just to give it a bit of a rest - basically grounding the energy of the deck.
That's just what I would do personally, though, so with some trial and error I'm sure you'll figure out what works best for you
