Array.slice() Not Creating An Independent Copy.

Alright, am I missing something?

I create a 2D array like so:

var blah = [];
blah[0] = ['one', 'two', 'three'];
blah[1] = ['four', 'five', 'six'];

Then I *attempt* to create an independent copy based on all of the pages I have read that
said it was as so:

var copy_of_blah = blah.slice(); // does not create independent copy
var copy_of_blah = blah.slice(0); // nor does this

I tested it by immediately changing either:

blah[0][0] = '' // "one" is now ''

*or*

copy_of_blah[0][0] = '' // "one", is again, ''

And of course both reflect changes upon the other.

Is it possible to create an independent copy of an array without having to write a
function that dumps the contents into a new array?