Something like this should work (untested): 
sub insert_domain {
    my $cursor = shift;
    $cursor = $cursor->{$_} ||= {} for @_;
    $cursor = {};
}

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

[download]

The only "trick" here is using ||=, which only assigns to a variable if it's false. Since we only add hash references in this hash structure and references are always true, it means we only assign an empty anonymous hash {} to nonexistant values; otherwise, we move the cursor down one level to the already existing subhash.

Update: pg's post compelled me to test mine, and it does work:

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' => {}
                                    }
                   }
        };

[download]

Makeshifts last the longest.

In reply to Re: storing domain info in hashes of hashes by Aristotle
in thread storing domain info in hashes of hashes by ajefferies

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