If you use a brass heating block (which is a bit heavier than aluminum), you can first use a heat gun to soften the residues to remove the cartridge/sensor.

After removing all electronics, you can use a gas torch and burn the residues off. However, the far best option would be to use a heat block made of stainless steel. I guess heat conductivity is anyway not very important on the hotend as long as the cartridge is powerful enough.

Using a torch makes cleaning very fast. In five minutes you are typically done.