Parse soap response and concatenate with another string

I have been using soapui opensource for a small period and not yet good at groovy script. Please help figuring out the following issue:

I get response from the previous test step. Lets say Response1 and need to parse it in order to get Idvalue from it. Then I need to add string DomainId before this id so that it looked smth like this:

DomainId_234565

and tranfer it to next request. Could someone please explain how to do it with groovy? (I guess it is the best way to do it)

Thank you