Please don't rub them or scrape them with anything. In fact you need to avoid any mechanical cleaning completely.
If they have heavy dirt I'd just soak them in fresh water with some dishwahing detergent, on edge in a glass (nice and sudsy).
Take them out after a day and rinse them under the tap and gently blot them dry.
You might just try soaking them in fresh water for a couple days and see if the gunk disolves in the water.
If they have heavy black sulfide on them you could use an electrolytic reduction bath but you still need to wipe the black away and if they're good quality coins even that could screw them up.
What does the grime look like? Can you post a couple pics?
Don't be in a hurry to clean them. Sit tight until you know if they even need to be cleaned.