/scoreboard players set @a[score_justDied_min=1] justDied 0

The above command will not set a dead player's score to 0 if dead, but will work when next alive. In 14w17a, this will match a dead player and set their score to 0.

This was particularly useful for /execute when a player had died, to summon a mob on their death location or drop certain items on death (and only once, whereas now it will continually summon an entity until they respawn)