On Qubes it results in kernel message: sysrq: SysRq : This sysrq operation is disabled.
Default value of /proc/sys/kernel/sysrq on Qubes dom0 is 16. Changing to 1 does not work either:
And finally shutdown after timing out for every VM - 20s per VM. Not good, at least.
Sysrq-c makes dom0 frozen for some time (5s?) and then reboots. Also after changing sysctl setting.