Remember ... scratches don't add value. I'd no sooner use a toothpick any more than than I would a wire brush.
The contaminate is tape residue. If it's mucilage ... old "hide glue", warm water may be more effective than acetone. Even if it's a more modern glue, It can be removed without anything touching the surface of the coin. Using thorns, toothpicks, and even q tips ..invites scratches ... some larger than others ... but all equally undesirable.
Air is still the best tool. The effectiveness of masking tape will also amaze you.
Bet Dave won't want it near as much with scratches on it.
Chance