Read Target group's managers and send mail to email attribute value defined in other domain

Hi ,

We have Domain A and Domain B in ARS. Domain A and Domain B users are in sync. Domain A does not have email attribute or incorrect email attribute but corresponding user in domain B has correct email attribute. we have security groups in domain A only and Managers and secondary owners defined in that.

Now i need to start workflow on group modifications requests in domain A . We will create workflow to assign approver rights to Manager and secondary owners for group and send email to approve the request. now since email attribute in domain A is null and corresponding managers in domain B have correct email attribute. how can we map so it read email value from domain B for each respective managers of security group in domain A? 

Appreciate for any help in this regard.