Return to Greece for tax deposits abroad.

Regarding the tax return the interest on monies held overseas is the prohibition on double taxation? Ie when something is taxed in a country member of the EU normally under the existing contract between the countries, may not be taxed in Greece. Ie If someone has such account in Germany and is withheld from interest therein may not be withholding tax in Greece, so the owner does not owe anything on Greek state. This is so or not applicable to deposits?
This is a comment on " Balances with banks abroad "