A.t

use Test::More;
use Module;

is($Module::data, undef);
$Module::data = 10;

done_testing();

B.t

use Test::More;
use Module;

is($Module::data, undef);

done_testing();

do.pl

#!/usr/bin/env perl

use strict;
use warnings;
use Sub::Fork qw( fork );
use Test::More;
use Moose;
no Moose;

my ($file) = @ARGV;

foreach my $file ( @ARGV ) {
    fork sub {
        do $file || die $!;
    };
}

Module.pm

package Module;

our $data = undef;

1;