It depends on the oxide. If it formed slowly it will be quite smooth and will adhere fairly well. With time and care, you should be able to get the dirt off without much disturbance. However, as I said before, be very careful on edges of the coin and lettering.

If the oxide is rough, then any effort made to remove it will probably leave some pitting below it. The question to ask is does it look better with an oxide blemish or with a pit.

One thing mentioned was electrolysis. I've never used this myself on copper coins, but a job I once had required a lot of work with what was called coulometric reduction, another phrase for electrolysis. Some things we learned about this were that high current densities (greater than about 75 microamps/sq. cm) would cause corrosion to flake off rather than be converted to copper. However, at our standard 50 microamps/sq. cm, the process would sometimes not initiate. Therefore, we would start at the lower value and if no reaction initiated, we would run up to about 100 microamps/sq. cm for a minute and then back off to 50 again. I think the higher values cause the generation of so much gas within the oxide, that it didn't have time to leak out and instead built up pressure which blew off the oxide.

Even at it's most successful though, the electrolsys always left a somewhat frosted appearance. It is never possible to convert the copper oxides back to pure copper completely and in its original shape.

What I guess I'm saying with all this rambling is electrolosys is useful when the physical approach doesn't work. The best thing is to find a few wheaties with some bad corrosion and experiment with them. Don't be in a rush to attack the large cent if you've never done one. It's been in the ground a long time. A few more days or weeks without cleaning won't hurt it. By the way, if you check photo forum from just after the the 4th of July (around the 7th to 10th I think), you'll see a photo posted by someone else for me. It has 9 large cents found together, and the corrosion on some was pretty bad. All were cleaned with olive oil, toothpicks, and even a metal nut pick which can clean off surface oxide without scratching the surface is done properly. Good results are possible, but it takes some time. Good luck and many more large cents (and silver and gold).