I got an exception when setting up mysql replication on one of my servers:

mysql> grant replication slave on domains.* to replicator@'%' identified by 'hidder-password';
ERROR 1221 (HY000): Incorrect usage of DB GRANT and GLOBAL PRIVILEGES


[Solution]
After search around, got the point... REPLICATION SLAVE is an administrative privilege, so I have to grant on *.* like this:

GRANT REPLICATION SLAVE ON *.* TO 'replicator'@'%' IDENTIFIED BY 'password';