There's actually nothing to stop the EU declaring that all accounts anywhere in the EU belonging to a Greek national (say) get redenominated in Drachma.
I don't believe that would be legal under most EU countries' domestic banking laws, not to mention EU law. For example, I'm a non-Danish national (American) with a Danish bank account, and under Danish law the government could not treat my bank account in a disadvantageous way (such as confiscating it, or unilaterally redenominating it) solely because I'm American. They could pass a law forcing me to close the account (e.g. by tightening the rules on foreign-owned bank accounts), but they would have to let me withdraw my money if they did so, in the same currency as it's denominated in (DKK).
It wasn't "legal" for countries to stray from the stability pact either, but they did! We're in the realm of making stuff up as we go along here. Or the Greek government could declare it illegal for Greeks to hold bank accounts elsewhere. Certainly it's not tenable for the average Greek to squirrel away all his or her money in German banks, waiting for the "grexit", then cashing in.
It's not tenable but I suspect it's what's happening.
Actually it's what's been happening in Greece since WWII. First you have fascist governments that you don't trust and then you have democratic governments that want you to pay tax. Greeks have long been used to keeping their money where the government can't find it - in US$ under the bed or in Euros in German banks.
The situation in Spain at the moment seems to be that every Euro sent in the bailout is removed form a Spanish account and paid into a German bank. Spaniards speak Spanish, they read Argentinian newspapers when their brilliant economists 'solved' their currency problem by seizing the accounts of everyone who wasn't a ruling General.
Well, the Greeks freely voted for politicians that promised lavish spending from the public purse - I don't think they deserve too much sympathy for the taxes to pay for it all.
When did US voters last pick a government that didn't promise tax cuts and then increased spending ?
But that's not the point - the point is that there isn't very much you can do at this point to stop Gresham's law in Greece/Spain/etc. Short of building a wall searching people at border Greek 'money' is going to be flying out of Greece at the moment, whether it's to Euro savings accounts in German banks or US$ held by their brother/cousin/uncle in New York.
