Split one galera cluster into two galera clusters

[PS]

Hi, 

I've a galera cluster of 3 nodes compound of two main databases (~200GB per DB) and some smaller DBs. HAProxy is used as the entry point of GC.

I'd like to split this cluster into two independants clusters to lower the time of making a node back into the cluster in case of SST.

What is the correct way to do it minimizing down time?

Best regards, 

-- 

PS