Questions about Global Currency

Is a global currency possible as a solution to the global banking crises? If so, how would that work? Would we trade-in our tired, worn-out and worthless dollars, euros, francs and pounds - getting a percentage worth of the new currency? Like a in a bankruptcy, where vendors are only paid a fraction of what they're owed, would we have to trade in the value of out dollars for the new and lower value money? How are the going to do that?