# define the anon arrays here instead of in the child
foreach(@doms)
{
    $mxs{$_} = [];
}

for( 1..$PREFORK )
{
    last unless @doms > 0;
    my $url = shift @doms;    
    child( $url ) if !fork();
}
 
wait(); # wait till one dies;

my $kid;
{   
    if( @doms > 0 )
    {
        my $url = shift @doms;
        child( $url ) if !fork();
    }
    $kid =  wait();
    redo unless $kid == -1;
}

print Data::Dumper->Dump([\%mxs]); 
exit;