Firstly kudos to the excellent posts from Edwin Biemond - which were my starting point here -
also a BIG thanks to my colleague FlaviusS for the SAMLCredentialMapperProvider setup.
In this scenario, I create a web service and deploy it to WLS server running in nc_domain.
I then create a SOA composite with a BPEL process that calls this service.
The SOA composite is deployed to bpmps6_domain.