The DFU partition is a specific area of memory where the SUIT envelope is stored, as defined in the devicetree source file.
The following command cleans up the DFU partition and the DFU cache partitions on the device connected to the serial port COM7 on Windows (run nrfutil device list to check the serial port name for your OS):
nrfutil suit cleanup --serial-port COM7
This command performs the cleanup and produces no additional output.