If we consider homology between two nucleotide sequences as a yes/no answer to whether they have shared a common ancestral sequence, then given that all life share common ancestry and sequences are carried by living things, then how can two biological sequences be anything but homologous?
One possibility I can think of is perhaps natural transformation in bacterial---but even so, the DNA sequences picked up must have come from a biological source.
(I assume that it must be possible that there are sequences that are non-homologous, because otherwise there wouldn't be a need to point out which things are homologous, i.e. I assume that the concept of sequence homology would not be as widely used as it is right now)
There has been some discussion on my claim that homology should take a Boolean value. As I have stated in the comments, for this I refer to Inkpen, S.A. & Doolittle, W.F. J's "Molecular Phylogenetics and the Perennial Problem of Homology" in Mol Evol (2016), pp. 187.
Nevertheless, there is a general understanding that conflating the extent of similarity and the inference of common descent is always a misuse of the concept—that there can be no such thing as ‘‘percent homology.’