c:\@Work\Perl>perl -w -MData::Dump -le
"$REFERRERS{foo}{bar}{baz}++;
 ;;
 dd \%REFERRERS;
"
{ foo => { bar => { baz => 1 } } }

c:\@Work\Perl>perl -w -MData::Dump -le
"$REFERRERS->{foo}{bar}{baz}++;
 ;;
 dd $REFERRERS;
"
{ foo => { bar => { baz => 1 } } }