use strict;
use warnings;
use Data::Dump::Streamer;

my $location_hash = {
    'New York' => {ZIP => '123-456-789'},
    'Dunedin' => {ZIP => '9001'}
    };

for my $city ( keys %$location_hash ) {
    print "$city $location_hash->{ $city }->{ZIP}\n";

    delete ($location_hash->{ $city });
    delete ($location_hash->{ $city }->{ 'ZIP' } );
}

Dump $location_hash;

##</code><code>##

Dunedin 9001
New York 123-456-789
$HASH1 = {
           Dunedin    => {},
           "New York" => {}
         };