Here is a way:
ineq = 0 <= Subscript[u, a] <= 1 && 0 <= Subscript[v, a] <= 1 &&
0 <= Subscript[u, b] <= 1 && 0 <= Subscript[v, b] <= 1;
FindInstance[setA == setB && ineq,
{Subscript[u, a], Subscript[v, a], Subscript[u, b], Subscript[v,
b]}] // FullSimplify
inters = FullSimplify[setA /.
Solve[setA == setB && ineq]]
Show[{ParametricPlot3D[{setA, setB},
{Subscript[u, a], 0, 1}, {Subscript[v, a], 0, 1},
PlotStyle -> Opacity[.5]],
ParametricPlot3D[setB,
{Subscript[u, b], 0, 1}, {Subscript[v, b], 0, 1},
PlotStyle -> Opacity[.5]],
ParametricPlot3D[inters[[1]],
{Subscript[v, b], 0, 1},
PlotStyle -> Directive[Thickness[.01], Red]]},
PlotRange -> All]