I guess that you want to re-generate the whole image, don't you? If so, you can try the following commands to ensure that bitbake won't use the sstate cache:
bitbake image-name -c cleansstate && bitbake image-name
In the case you just want to rebuild the kernel, substitute image-name by virtual/kernel (or the name of whatever recipe you want to rebuild).
Note that the do_cleansstate task is going to remove the recipe ${WORKDIR}!
For further information: https://www.yoctoproject.org/docs/latest/ref-manual/ref-manual.html#ref-tasks-cleansstate
In the case you're doing such modifications directly in the ${WORKDIR}, which you shouldn't unless you're testing, the execution of the following command would be enough:
bitbake virtual/kernel -f -c compile
or
bitbake virtual/kernel -C compile (to invalidate the stamps and force all tasks starting from do_compile)