I think it would be reasonable to reduce the tax by the amount of foreign tax paid, but I don't think it would fix the problem. Most of the money in offshore havens was barely taxed. So instead of 35%, Apple can pay maybe 30% bringing it home. That's not enough of a drop to motivate them. It would probably open some more loopholes, too, but I can't be sure about that.

The real issue is that some countries want to allow this stuff. They want these shell companies because it brings them some revenue they wouldn't otherwise have. And who can blame them, really. So as long as we have international companies, we'll have tax havens. I'm not sure if there really is a fix.