Upgrading DB Schema to multiple Mysql Instances automatically

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Hi Guys,

I have multiple Mysql DB instances containing same schema but different data in the tables, running in my unix server.
I always have the issue of not upgrading all the instances at the same time, this leads into inconsistent of DB schema.
My question, is there any tool/script that can sync all my DB instances automatically once i upgrade one instance.(Sync only at schema level not data).
I have heard about Mysql replication,but can it sync only schema and i consider each instance as independent because i run application on every instance.!!
Please let me know if I am not clear with the above message.

Cheers