Dmitry A. thoughtfully pointed out an option to transfer files across domains with scp, assuming there is an intermediate ssh server.  Here is an example from a STAR OLP machine to one of the STAR database servers:

[onl03] ~/> scp -o 'ProxyJump wbetts@rftpexp.rhic.bnl.gov' /etc/services root@db05.star.bnl.gov:/tmp/from_onl03_via_rftpexp_ProxyJump

Note though that the ProxyJump option was added to openssh in version 7.3.
Red Hat EL 6 and its derivatives have openssh-5.x as the stock packages, so will not have this option available.