@acquire<EOL><INDENT>def flush_all(self, conn):<DEDENT>
command = b'<STR_LIT>'<EOL>response = yield from self._execute_simple_command(<EOL>conn, command)<EOL>if const.OK != response:<EOL><INDENT>raise ClientException('<STR_LIT>', response)<EOL><DEDENT>
Its effect is to invalidate all existing items immediately