XE166 TRAP Interrupt clearing

Ref: xe166m_um_v1[1].2_2008_09_vol1sys.pdf
{XE167xM/XE164xM/XE162xM Derivatives System Units (Vol. 1 of 2)}
> Page: 8-183
> Text: "Note: When servicing an SCU trap request, make sure that all related 
request flags are cleared after the identified request has been handled. To clear 
a trap request that is stored in register DMPMIT, first clear the request source 
of the source, clear the request within DMP_M via DMPMITCLR, and then clear the 
request within DMP_1 via TRAPCLR."
>
> Question: what is meant by "request source of the source"? Unable to clear 
DMPMIT or TRAP without this step.