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