MySQL 4.1.14.
If you can not drop a user because you get the following error:
mysql> drop user 'username'@'domain'; ERROR 1268 (HY000): Can't drop one or more of the requested users
Revoke all privileges first:
mysql> REVOKE ALL PRIVILEGES FROM 'username'@'domain'; Query OK, 0 rows affected (0.00 sec)
Then drop the user.
mysql> drop user 'username'@'domain'; Query OK, 0 rows affected (0.00 sec)