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nah, rub it with steel wool, it'll be fine
but yeah, soaking it in warm water and blotting it with a cloth should work.
The one big problem with suggestions like that is the incompleted details. For one thing just what grade of steel wool should be used? Would a Brillo pad work?

Might want to go to Starbucks and tell them your going to have a law suite about their coffee ruining coins. Might get a new proof set from them.

Go to a store and see if in the cleaning product aisle anything states removes coffee.

Sent to the Mint and complain

Spend them and make some kid happy.