If you'd like to detect for somebody at a specific location, use the location selectors (`x=[x co-ordinate]`, `y=[y co-ordinate]` and `z=[z co-ordinate]`.)

Your selector should look sometihng like this:

    @a[r=1,x=0,y=0,z=0]

This command detects for players at 0, 0, 0.

The `r` specifies the radius to detect. Set this to `1` as you do not want to detect others in adjascent jobs.  
The `x`, `y` and `z` as above stated: Specifies the location to detect it from.

**Note:** You *cannot* use relative locations when providing co-ordinates in selectors.

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Seeing what you're trying to do:

>I'm looking for a player within 10000 blocks of the command block, with a wool in his inventory that's standing right underneath (or at least, with his head in) the command block.

You're better off using a scoreboard clock to test for whether the player has the wool in his inventory, then add that scoreboard selector into your command.

    /execute @p[r=1,x=0,y=65,z=0,scoreboard_hasWool_min=1,scoreboard_hasWool=1] /effect @p invisibility 12 3 true

The above command assumes that you're testing for a player standing on the block `0, 64, 0` and the name of the scoreboard detector is `hasWool`.

Also, set the co-ordinate to be **one block above** of the block you want the player to be standing on, as entering the block's co-ordinate will only detect if they're in (and not on) the block.