Actually on all new Intel desktop boards, there is a new features called ProcHot and it is the CPU Die temperature. It is within the range of 0 < Temperature < -100 Celsius.
temperature at which the CPU will start throttling itself in order to remain cool enough.
Throttling means skipping clock cycles.
If it is showing ProcHot -21 C, it indicates that the cpu have 21 degrees to go to make the cpu to start throttling itself.
If it returns 0, the CPU will assert prochot and start throttling.
So since you are using the new Intel Desktop Utilities, it will use the same principle to calculate the temperature and display it in the chart/diagram.
So what you can do, check the CPU temperature in the BIOS, from Advanced >> Hardware Monitoring.
Check the Thermal Specification for the CPU if it is still within the range of operation.
Get your CPU sl number and search in the link below.
If it is much over the range then, check the following:
Make sure that you have a PSU Atx Version 2.2 at least.
Make sure that the chassis is TAC - Thermally Advantage Chassis
Check for proper aeration in the chassis. (cable)
Re-integrate the cpu with new small amount of thermal paste (clean the cpu before)
Hope this helps a bit.