How to filter private IP space from DNS_RESPONSE

I started with this :

  when DNS_RESPONSE {
    if { not [class match [IP::client_addr] eq "local_net" ] } { 
      foreach entry [DNS::answer] {
        if {[DNS::type $entry] eq "A"} {
          if { [class match [DNS::rdata $entry] eq "private_net"] } {
             need to return not found here
          }
        }
      }
    }
  }