Attacks from your secondary build domination quicker than holds from your primary. Not sure about attacks in the primary although there aren't that many of them anyway.
My MA IDs:
Fiend Space: 211464
Your secondary does build up Domination... and /Psi especially so. 
If it has eyes, you can blind it, if it has blood, you can make it bleed, if it has a mouth, you can make it scream.
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/Psi especially so.
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Yup.
With a little recharge you can turn psi dart into a psionic machine gun! :O)
My MA IDs:
Fiend Space: 211464
aah ok thats cool that'll explain why my friend thinks that Fire/psi doms are farming experts or something! 
Would secondary immobolization/hold attacks build up domination as well as primary? For example I just rolled a Grav/Psi dom and I was just curious if an attack such as Subdual would also build up domination since it does more base damage than Crush, or is it only primary attacks that builds up domination?