The scan is triggered by the crontab entry for your site.
# /omd/sites/test/etc/cron.d/cmk_multisite
# Run Multisite regular jobs, e.g. scheduled reports
* * * * * . $OMD_ROOT/etc/omd/site.conf ; curl http://localhost:$CONFIG_APACHE_TCP_PORT/test/check_mk/run_cron.py >/dev/null 2>&1
I checked on one of my test systems with a actual CMK. It is working without problem.
Is your system a distributed setup or a single standalone installation? Or better said if CMK sees your site as a slave then no scan will happen.