The first thing that needs to be done is to see what kind of encrustation it has, is it the orange rusty kind like on iron (which I'm pretty sure you are talking about) or something else like light surface encrustation. Photos of what kind of encrustation it has will help find an appropriate method. I'm not sure that hydrogen peroxide will work on silver, the chemical reaction that will help copper does not work as good on other metals. I think that a good method may just be to boil a cup of water, drop that coin in and wait for a couple minutes, since the encrustations are chemically separate from the coin (unlike, for example a nail, which the rust almost become part of) it may work just to pick them off when a toothpick or your fingernail. Underneath the encrustations the coin will fine, maybe a slightly different color though. In my experience it is much harder to remove encrustations from copper or brass than silver because silver does not experience the same degree of corrosion. One other method that may work is to just soak the coin in lemon juice with salt added, let it sit for a little less than a day or so checking on it frequently. This may also loosen the encrustations and you could then just make them come of with a toothpick. The lemon juice will give it a more unnatural patina removing some of it's natural patina (many people seem to kind of like how it looks though, but cleaned coins will be less popular with collectors), what would you want though, horrible looking pitting or a slightly brighter surface? I recommend trying that if the coin is in rather bad condition, you could maybe try the first method first though and try this next though. I do not have much experience with silver coins though, when I find silver all I need to do is rinse it off and it will look good as new, even after 200 or so years of being underground. Electrolysis may work but I'm not the guy to ask on that, last time I did it I created dangerous chlorine gas, I closed the door of that room and opened the windows to let out the fumes. I'm pretty sure that there will be someone to help you that does know how to do it correctly. I have heard electrolysis to sometimes cause pitting on very corroded coins, though those coin are usually pretty bad, like I said, a photo may help determine what state it is in.
Is this the kind encrustations on the coin?
Here are some rust encrustation on a brass button, these were the kind of encrustation that I was talking about. Is that the same thing?
If your coin look like the coin below (not my photo) I'm not sure that there is much that can be done, electrolysis may help a little though.
) (something along those lines)
