[Exim] Making a blackhole router...

I'm having a spot of trouble and going round in circles trying to get a
specific set of (non-local) mail blackholed... (an antivirus solution
which sends warnings back to the sender of infected mail, which these
days isn't always the source of the virus :/ ).

Because I'm using exim 3.36 and I only want to blackhole non-local
instances of this mail warning, I've created a router which only takes
effect for the mail in question; it's just I can't figure out how to
neatly blackhole that mail when I've detected it.

The best I have so far is using

route_list = * 127.0.0.1 byname
self = fail

as part of my domainlist router--which works, but gives some rather
unslighly log messages as the mail is dealt with. Is there a cleaner way
I've overlooked?

DG