How to get the current org's domain in a flow

 
LEFT($Api.Partner_Server_URL_470, FIND( '/services', $Api.Partner_Server_URL_470))
[9:41 PM]
that gives me a nice 
https://customer-customization-9925.cs2.my.salesforce.com/ URL
[9:41 PM]
I think you can create a formula variable in your flow and use it