syncing - between databases

I need to maintain a sync-ed table across several databases. For example I
have a customer table in 5 databases. If a user of any of the databases
inserts a new customer I need to insert the new record into the other four
databases. But question is updates and deletes.

I can use a trigger and dblink to update the other databases when the action
is an insert because in each of the other databases I don't have to worry
about a locked record. But what happens if a user is updating at the same
moment as a different user in a different database is updating the same
customer. Can a race condition occur?

I was thinking I could create a master database. And have all the other
databases use dblink to excute the master trigger.

Any advise would be helpful,

Johnf