You'll need a chroot for each of the secondary architectures.
This is somewhat tiresome,
even though Debian has excellent tools for managing chroots.
-C<sbuild-createchroot> from the sbuild package is a
-good starting point.
+C<sbuild-debian-developer-setup> from the package of the same name
+and C<sbuild-createchroot> from the C<sbuild> package are
+good starting points.
Otherwise you could deinstall the packages of interest
for those other architectures