Two sites with the same subdomain in tow various domains - is that possible?

I would like to ask, is that possible to create two sites having identical subdomains in two different domians, for example:

FooBar.domain1.com - site1
FooBar.domain2.org - site2

Now, if I'm trying to register the same subdomain in second domain, the stsem says, that such domainname is already registerd

If this is really impossible, in my opinion, whole idea of multiple domains losses it's sens, because it wastes possibilities Multiple domains makes sens only if they allow users to register more blogs using popular words. For example if someone names John, then only one John will be able to have "john" subdomain, even, if in the rest of domains such name is available.

Please tell me how to override that problem, or maybe do some enhancements on that.

Thanks,
Karol Kossut