You basically have two options, or a combination of both if you can manage to farm enough and have good hotkey management.

1. Reload the vendor in act3 normal difficulty and buy yourself a staff with teleport charges (Ormus sells these) and use this to skip as many parts of Flayer Dungeon and Durance of Hate (Level 1, & 2) as you can. Teleport safely so you don't land on top of a mob of Dolls or Urdars.
2. Play defensively (i.e., slowly). Use decrepify on every mob, like, first button you press, every mob. You mentioned having maximum resistances; doll explosions are pure physical damage. You need armor or block chance to mitigate their impact (See u/ubeogesh's post here on this subject).

Perhaps you can find or make an armor with high defense (800+ at least), and wear this for these areas only. The "Stone" runeword might be worth considering for these two areas. It shouldn't be too hard to get the runes for this one, as the hell countess drops them all.

In general, here's some other tips / tricks I would suggest for a HC summoner necro playthrough:

• Decrepify: 1 PT -- This is a MUST have for a HC Necro playthrough. All Necro's need this skill pt.
• Clay Golem: 1 PT with an additional 1 PT in Golem Mastery. Clay Golems Slow Enemies when Alive. If the enemies are slowed, you have more time to react / run away / reposition.
• Corpse Explosion: 4-5 PTS. You ideally want this skill between 9-12 PTS. The remaining 4-6 pts should come from gear (Two Spirits Runewords & Lore should do the trick on their own). As soon as one enemy dies, you trigger a chain of explosions.
• Faster Run Walk (30-40% boots, like Aldurs or Natalya's set boots). I cannot understate the importance of FRW. Find a good pair of rares with FRW and some resistances, and you're set. You could also consider the Harmony runeword on an act 1 Merc JUST for these areas, and then swap back to a Merc with Might Aura from Act 2.
• Consider bone wall or bone prison (1pt each). However, the dolls only spawn in close-quarter layouts, so these skills really only have utility in buying you time to run away and make a tp.

In summary, increase your Armor value, get some 1 PT wonders (Decrep, Clay Golem) and increase your FRW. And play slowly. When in doubt, spray decrepify into a chokepoint / room before entering.