That is to be expected. Your top hash contains references to hashes; you need to dereference them first. To do so you need a nested loop:

foreach my $key (keys %hshFoo) {
    foreach my $subkey (keys %{$hshFoo{$key}}) {
        print "$key/$subkey => $hshFoo{$key}{$subkey}\n";
    }
}
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See perlref, perllol and perlreftut.

Makeshifts last the longest.