[Exim] how to check if domain doesn't point to local host

Hi,

I have
domainlist local_domains =      lsearch;/etc/mail/locals : \
                                lsearch;/etc/mail/virtuals

send_to_gateway:
driver = manualroute
domains = ! +local_domains
transport = remote_smtp
route_list = * mygw.pl
no_verify

/etc/mail/virtuals is autogenerated and here is the problem that sometimes
this file contains domain which is not hosted on local host.

The question is how to add condition based on no idea what (dnsdb?) that will
check real A and MX of that domain.

send_to_gateway:
driver = manualroute
condition = check_if_domain_is_on_remote_host_even_if_it's_in_local_domains
transport = remote_smtp
route_list = * mygw.pl
no_verify

Any hints?
--
Arkadiusz Miśkiewicz    CS at FoE, Wroclaw University of Technology
arekm.pld-linux.org AM2-6BONE, 1024/3DB19BBD, arekm(at)ircnet, PLD/Linux