Haneesh, I am having the same issue. I am using Qlikview 9 SR3 but we are preparing to upgrade to version 10 soon. We have multiple business units under different domains and would like to be able to manage access using the parent domain.
I look forward to a response to this issue from Qliktech.
We tried using the parent domain too, and it did not work. Then we found out that we could add as many domains as we wanted by going to QEMC > System > Setup > Directory Service Connectors then clicking on the Directory Service Connector name icon and then Active Directory (for those who haven't tried it yet). On the right side of the screen, you can add as many domains as you want. Then you can see all of the user names when you set up a document.
Even with 23 domains, it seems that the individual listings will be easy to maintain - it only takes a minute to add or remove one - and you get a lot more control. For instance, you may only want some of the child domains to have access to QlikView, and you can just enter the ones that need access.
We are also on QlikView 9 SR3.