RDM has said that it was most definitely Earth.
From the previous page...
http://featuresblogs.chicagotribune....dee-.html#more
Lots of interesting info. They actually have articles each week, with interviews with the writers etc.
Here are the ones for The Oath & Blood on the Scales:
http://featuresblogs.chicagotribune....igh-gaeta.html
http://featuresblogs.chicagotribune....es-angeli.html
[The one for "Blood on the Scales" obviously has spoilers for anyone watching it on Sky]