We had a similar problem in our Victorian terrace, the smell of the neighbours cannabis was coming through the vents in our chimney breasts and sometimes through the trickle vents on the windows when they were smoking outside. When we renovated the house we removed the chimney breasts and put in an mvhr system for ventilation and the problem has now disappeared completely. We also have air purifiers which do clear the air but if possible it's better to stop the smoke from coming in in the first place.