How to find out the currently active linux virtual terminal while connected via ssh?

The situation is as follows.

I have a multiuser desktop machine with Debian Linux 6.0 and an ATI videocard with one monitor connected. I have root access to it. There can be several KDE sessions started, like this:

$ w
 21:51:30 up ? days,  4:22,  ? users,  load average: 1.72, 1.68, 1.67
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
u1       pts/0    :0               Sat18    4days  0.00s 11.68s kdeinit4: kded4 [kdeinit]                      
u2       pts/5    :1               Mon17    2days  0.00s  6.65s kdeinit4: kded4 [kdeinit]                      

So, two virtual terminals are in use, tty7 and tty8:

$ ps aux|grep /usr/bin/[X]
root      2944  3.1 12.4 670040 1019904 tty7   Ss+  Aug27 187:52 /usr/bin/X :0 vt7 -br -nolisten tcp -auth /var/run/xauth/A:0-??????
root      5507  0.9  3.7 425136 309676 tty8    Ss+  Aug29  29:38 /usr/bin/X :1 vt8 -br -nolisten tcp -auth /var/run/xauth/A:1-??????

But of course only one of them is active at any given moment, i.e. displayed on the monitor. Someone sitting at the keyboard can switch between them using Ctrl+Alt+F[78]

So, I connect via ssh from a remote host. I need to know which X DISPLAY is active now. Is it possible? I have googled all over the place and can't find the answer.