Two master databases for two separate apps
MULTIMASTER SETUP
I would recommend a multimaster setup only with the idea that you restrict Asia's data to one master, and Europe's data to the other master. As for the shared databases, make sure auto_increment_increment and auto_increment_offset are in full use. In addition, make sure you only write Asia's data to the shared databases at the Asian DC and likewise with Europe.
STORAGE ENGINE CONSIDERATIONS
If there is no specfic reason to keep MyISAM (such as FULLTEXT indexing or heavy volume reads), I would recommend converting everything to InnoDB. That way, if a server crashes, then crash recovery can bring databases to a consistent state. With MyISAM, tables can be left in a crashed state and repairing those tables may result in the disappearence of one or more rows of data.
HIGH AVAILABILITY
You should strengthened your HA Setup by implementing DRBD. DRBD should be setup as at each DC. What are the benefits?

You maintain a disk-level replica of the mysql data within both data centers
You can have automatic failover within each data center
You only worry about MySQL Replication between DCs

REPLICATION
To minimize data loss with MySQL Replication over geographic distance, I would recommend using smaller binary logs. By default, a binary log/relaylog is 1G (max_binlog_size and max_relay_log_size). You can make these values much smaller. I got this idea from PostgreSQL because WAL files are 16M by default. This creates more log files, but those log files will be closed and complete faster on the acting slave. If you are not using it, you should upgrade to MySQL 5.5 because it has Semisynchronous Replication. It can be tuned to detect heartbeat timeouts with some granularity.
I wrote about some of these concepts in an earlier post back on March 29, 2011.