my @list = qw(
              .coop
              .com.co
              .com.mv
              .com.fj
              .com.sb
              .com.nf
              );
@list= sort {
    my (undef,$sub1,$tld1)=split /\./,$a;
    my (undef,$sub2,$tld2)= split /\./,$b;
    warn "[$sub1].[$tld1] cmp [$sub2].[$tld2]\n";
    $sub1 cmp $sub2 || $tld1  cmp $tld2
} @list;

print "$_\n" for @list;
__END__
.com.co
.com.fj
.com.mv
.com.nf
.com.sb
.coop