car registration Germany and deregistration Greece (Munich)

Perhaps a Greek in Germany may have an answer to this question ie I have now registered my Greek car in Munich and changed the number plates. My question is how to deregister the car in Greece - preferably without going there. Does anyone know the process/contacts in Athens (or maybe its Pallini since we lived in Marathonas and the tax office for that area is Pallini...not sure if that means we have to deregister the car in Pallini too).THANKS