You need to use references to avoid the flattening you noticed:

my ($a, $b) = getarrayrefs();
print join(" ", @{ $a }), "\n", join(" ", @{ $b });

sub getarrayrefs {
  my @foo = (1,2,3);
  my @bar = (4,5,6);
  return \@foo, \@bar;
}
[download]

Phil

Update: Corrected sub name to match call. Thanks Albannach.