Every Windows Phone user know how to hard reset the Windows Phone, we just go to Setting > About > and click on Reset your Phone.
However WinUser.ir has discovered another special way to hard Reset the Phone, which will reset the phone to default factory setting and will not delete your Map data, retail mode content and customization data, however user generated data will also be deleted.
In the dialer just type : ##777#
After this, Below warning will popup.
This is really very good way to Reset the Windows Phone if your Phone is responsive and you want to preserve your Map Data and probably network setting, however if your Phone is unresponsive this feature will not work.
Thanks Winuser and John for the tip