script to find oracle databases that are not in cluster

I need to create a script to list all the databases that are in cluster environment.
The reason is that there are databases which are not in under cluster control and we need to identify those.
The easiest way to identify is:
clrt list (if SUNW.oracle_server:6, SUNW.oracle_listener:5 are not listed, then they are not in cluster environment)

but is there a better way and how to incorporate this into a script?
Our environment is quite big and I do have a list of all servers

thx