T@ta,
Como forma de resposta,para mim,é possível sim.Na interrogativa também é possível,e se alguém pergunta "Have you just done your homework?",com certeza algum tipo de resposta deve ser produzida,e a partir daí, podemos ter "No,I haven't just done my homework."
==>What are you writing now, or
what have you just finished? I have just completed two books: a sixth fostering memoir.(
http://www.andrewlownie.co.
uk)
==>And no,
I haven't just been busted,it's been over 18 months since my last lot of involuntary taxation.(
http://www.ls1.com.
au)
Actions completed in the very recent past (+just).a. Have you just finished work?
b. I have just eaten.
c. We have just seen her.
d. Has he just left?
http://www.edufind.com/english/grammar/Tenses4.cfmBons estudos!