sub insert_domain {
    my $cursor = shift;
    $cursor = $cursor->{$_} ||= {} for @_;
    $cursor = {};
}

insert_domain(\%domain, qw(org perlmonks www));

##</code><code>##

insert_domain \%domain, qw(com perlmonks www);
insert_domain \%domain, qw(org perlmonks www);
insert_domain \%domain, qw(org perl www);
insert_domain \%domain, qw(org perl use);
insert_domain \%domain, qw(org perl jobs);
insert_domain \%domain, qw(com perl www);
insert_domain \%domain, qw(org cpan www);
use Data::Dumper;
print Dumper \%domain;

__END__
$VAR1 = {
          'org' => {
                     'cpan' => {
                                 'www' => {}
                               },
                     'perl' => {
                                 'www' => {},
                                 'jobs' => {},
                                 'use' => {}
                               },
                     'perlmonks' => {
                                      'www' => {}
                                    }
                   },
          'com' => {
                     'perl' => {
                                 'www' => {}
                               },
                     'perlmonks' => {
                                      'www' => {}
                                    }
                   }
        };