What is the current ctrl-alt-backspace X win restart?

[Yasha Karant]

I have attempted to get a misbehaving X windows system to restart 
without rebooting the machine.  In the past, as I recall, 
ctrl-alt-backspace would do this.  This evidently has been disabled with 
the current X windows releases on Linux, including SL 6 .  What is the 
current equivalent (perhaps a shell command), or how does one reactivate 
a control sequence to force the X server to exit and 
restart/reinitialize, with a fresh login screen?

I have found some references using a web search to this issue for a 
number of current Linux distributions, but none of the offered "cures" 
seem to work with SL 6 (or presumably any RHEL 6 variant).

Yasha Karant