they can only move money into a Greek Bitcoin exchange
Sorry Ellie, that's not quite how bitcoin works. bitcoin is P2P money, each bitcoin owner stores it in a personal wallet, be it on their mobile, pc, usb or even as a physical coin/piece of paper. So unlike a fiat money created and owned by a private bank if you have physical possession of a bitcoin (or other Blockchain derived cryptocurrency) it belongs to you. So in that sense it's much like gold or silver, in that physical ownership is just that. Oh, and it's finite, so it has intrinsic value.
When you buy a bitcoin, or part of a bitcoin, 100 Satoshis, say, it is transferred from the sellers wallet to yours as a string of numbers. When you use your wallet to buy goods, those numbers leave your wallet and transfer to the vendor, so you can only spend your bitcoin once, it cannot be re-hypothecated.
You can, if you choose, store your btc in an exchange, but why would you given that Mt Gox and others have had their money stolen because of out of date/poor security.
Sorry if that comes across as patronising
I don't mean to.