Suppose a Greek shipping magnate decides he’s not comfortable keeping his wealth in Greece, and decides to buy some nice real estate in Berlin. (As if most of the Greek wealthy hadn’t removed as much as possible to Germany, the US and UK long ago.) He writes a check for €1m on his Greek bank to the buyer, who deposits it at Deutsche Bank. To settle the check, the Greek bank wires the funds from its reserve account at the Greek central bank, the Bank of Greece. The Bank of Greece instructs the Bundesbank to credit Deutsche Bank’s reserve account at the Bundesbank. Then the Bundesbank is owed €1m by the ECB, and the Bank of Greece owes €1m under the Target2 system (corrected).
There has been a lot of controversy about this process, and the notion that Germany will get stuck with massive losses if, following massive capital flight now in progress to Germany, the peripheral countries leave the euro.
A thought experiment: