You're very close.  jettero has already mentioned that you need to use the appropriate sigil; '$' instead of '%' for your hash.

You also are expecting a reference to a list in your subroutine hashOfArraysRef, but you have an extra level of indirection here:

&hashOfArraysRef(\$distri{$probExpr[0]});
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because $distri{$probExpr[0]} is already holding an array reference.  If you change it to this:

&hashOfArraysRef($distri{$probExpr[0]});
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you should find that it works closer to the way you need.