make clean all installed ports

[Peter Risdon]

I'm sure I saw recently on this list that it's possible to:

#cd /usr/ports
#make clean somethingorother

and clean just installed ports. A straight make clean in the root of the 
ports tree takes rather a long time.

But I can't seem to find the post anywhere. If this isn't the product of 
my feverish imagination, I'd be grateful for a reminder.

TIA

Peter.