Please please don't use a brush on the coins. That is a poor habbit to exercise. If it is just syrup try warm water as mentioned before. But do not use a brush, don't rub the surface at all.
I am sure glad you asked about this. I found 3 old Whitman folders that had scotch tape over the coins. Tape fell off, but left residue on the coins. Really hurt the silver. Oh there were 3 wheat cent ones, the same way. What a mess !