Don't be in a hurry to clean them, you may destroy the 'patina' that has built up over the years.
If you intend to keep them then, fair enough, do what you want with them, but if you're possibly thinking of selling them, then get professional advice first.
Brown sauce, ketchup, coca cola, baked bean sauce etc contain vinegar which is acidic. Soaking the coins in an acidic or vinegar mix (as Jayne mentions) will mean that any patina and dirt is easily removed by rubbing BUT please take Compman's advice first and check out their worth before removing dirt and patina.