Boiling is a big no no as air pockets can expand and cause the stone to explode. Bleach will be fine but will kill the moss of you wanted to clean it. Just be sure to thoroughly rinse with dechlorinated water afterwards.
If you want to keep the moss, I'd rinse really well with water coming out from your water change, then leave it sit in a tub of tank water with a bunch of snails from your tank (if you have any). I usually do a bleach soak, dechlorinated water, and then do the tank water soak with snails for a few weeks before adding to my tank.
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