Not in the cinderblock itself. The problem with the block is that the "rock" is so porous. I still recommend the bleach/water bath because of this. There could be dirt and stuff in the pores that you can't see harboring bacteria. Soak it in a bleach/water mixture and rinse it several times in hot water. You "could" bake it for around 30 mins @ 350* or so. I just like to make sure I get any dirt and things out of the rock first.
If you have a pot big enough to boil them in. That would just make me feel better as I like to make sure the only thing I put in there would be the "rock". Boiling should clean it out well enough and get any loose dirt or debris out of the block. Good idea.
***EDIT**** Just make sure you let them dry before baking them. Wouldn't want the concrete to explode or anything...