Avoding Cross-Domain Security Error Before Accessing Windowattributes?

I have a web application where window A opens window B (same site). B
later wants to do something depending on whether
the window A, window.opener.document.domain, has changed.

However, there doesn't seem to be a way to actually check whether A
has moved to a different domain without triggering (in IE) a security
violation and completely aborting the script. If the user has enabled
debugging, this also brings up an annoying dialog box.

I'd like to either catch this exception somehow or be able to tell
beforehand whether I can access window.opener.* attributes
successfully. According to:

http://msdn.microsoft.com/library/d...ng_security.asp

the only thing I can do is to *write* to the various attributes.

Can anyone suggest a way to work around this? I am not interested in
accessing the location/domain of the new page, just whether the window
has left my domain.