Forcing synchronization from SCCM Parent site to the child site can be done using the following way:
Logon to SCCM Primary site using account with full SCCM admin privileges and to run preinst command from:
C:\Program Files (x86)\Microsoft Configuration Manager\bin\i386\0000040
using the following switch:
preinst.exe /syncchild XXX
where XXX is a child SCCM code.
in my case MT1 is my primary child SCCM Server.
Check the following log files after launching preinst command:
Despool.log, Replmgr.log, Sender.log