MySQL Cluster Replication Merge We'd like to have two MySQL cluster groups, and at the same time have replication set up between them.  Is that possible?
Here are two possible setups you could try

TOPOLOGY #1


Data Center #1 with two(2) DB Servers (DB1, DB2)
Data Center #2 with two(2) DB Servers (DB3, DB4)
Setup DRBD with Each Data Center
Setup MySQL Replication Between the DRBD Primaries
Setup DBVIP (Linux Heartbeat/ Pacemaker / ucarp)


What this setup provides


Synchronous Disk-Level Replication Within Each Data Center
Asynchronous Replication Between Data Centers


TOPOLOGY #2


Data Center #1


Three(3) DB Servers (DB1, DB2, DB3)
Percona XtraDB Cluster among the three(3) DB Servers

Data Center #2


Three(3) DB Servers (DB4, DB5, DB6)
Percona XtraDB Cluster among the three(3) DB Servers

MySQL Circular Replication


DB3 used as Master to DB6
DB3 used as Slave to DB6
Use Semisync Replication Between Master and Slave



What this setup provides


Virtually Synchronous Replication Within Each Data Center
Asynchronous Replication Between Data Centers


I have discussed setups like this before


Feb 10, 2014 : MySQL High Availability for InnoDB
Jul 11, 2013 : MySQL replication between datacenters
Dec 26, 2012 : MySQL Replication and High Availability
Oct 25, 2012 : mysql read slave to fetch entire database on start
Aug 20, 2012 : Best solution for cross-datacenter MySQL master-slave replication
Mar 26, 2012 : 3 Databases, Best Replication Setup?
Dec 19, 2011 : Best way to setup master to multi master replication
Mar 29, 2011 : MySQL high availability, failover and replication with Latency


GIVE IT A TRY !!!