How to move Mailboxes from Exchange 2010 to Exchange 2013?

I know I need to install SP3 for Exchange 2010 and CU1 for Exchange 2013.

I two separate domains, in two separate forests.

To move mailboxes between these two separate infrastructures, would a Trust be necessary? Or can I simply follow these instructions: http://technet.microsoft.com/en-us/library/ee633491%28v=exchg.150%29.aspx