Identifying what kind of glue was used is certainly the first step. If it does not feel gummy or sticky it may very well be water soluble. People used to use glue like wallpaper glue or Elmer's glue in the old days to temporarily display their hobbies, with the idea of washing it off later and whoever did it just never got around to it.
Soaking the coin in distilled water may work. It may take a while since the glue would have crystallized by now, but it might be less harmful than solvents.
If the coin is precious to you, you may want to send it for conservation to NCS. It's amazing what they can do.