Heat some hydrogen peroxide in the microwave for about a min, without the coin of course, then let it soak for a bit. Periodically take it out, few minutes or so, and roll a q-tip with some of the peroxide on it to remove the dirt. keep going as needed.
I use this method for all my dug coppers and it removes the dirt very well.
rinse with water when satisfied.
this being said, your CRH find may have something other than dirt on it, so it may not work for you.
good luck