The Skirmish in the Dark Dimension was the first and final confrontation between Doctor Strange and Dormammu.
Having destroyed the London Sanctum and attacked the New York Sanctum, Kaecilius and the Zealots launched their final attack on the Hong Kong Sanctum. They found the sanctum protected by Wong and the Masters of the Mystic Arts.
Wong was killed in the resulting battle and the Hong Kong Sanctum was destroyed. With the final sanctum destroyed, Dormammu began to absorb Earth into the Dark Dimension.
Using the power of the Eye of Agamotto, Doctor Strange was able to reverse time, bring Wong back and restoring the Hong Kong Sanctum.
Kaecilius returned and confronted Strange, telling him that his actions were useless. Upon hearing from Kaecilius that the Dark Dimension was "beyond time", Strange figured out a way to defeat Dormammu and headed directly into the Dark Dimension.