I'll hazard a guess that your confusion stems from a single extra character in your code..

my $valid_names = &validateNames(\$names);
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You don't need the '\' before names. It's already a reference as returned by getNames, so you're actually sending a reference-to-a-reference to your function. Change it to:

 
my $valid_names = &validateNames($names);
# or even
my $valid_names = validateNames($names);
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and you'll be able to access the values in your validateNames function with:

  print $valid_names->{SCM555}{name};
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