my %tmp = map { $_ => 1} @foo;
my @uniq_foo = sort keys %tmp;
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I personally believe that you can avoid the intermediate step:

my @uniq_foo = sort keys %{ {map { $_ => 1} @foo} };
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Yes, it's a dirty trick! :)

And as far as your example with three arrays and the respective uniq'd incarnations is concerned, whichever way you choose, I would go with a HoA instead:

my %uniq = map {
    my %tmp = map { $_ => 1} @$_;
    $_ => [sort keys %tmp];
} keys %arrays;
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or

my %uniq = map {
    $_ => [sort keys %{ {map { $_ => 1} @$_} }];
} keys %arrays;
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or

my %uniq = map {
    my %saw;
    $_ => [map !$saw{$_}++, @$_];
} keys %arrays;
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or

my %uniq = map { $_ => [uniq @$_] } keys %arrays;
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